1. Field of the Invention
The invention relates to a method for the presentation of data from a storage medium for consumption by two or more users, in which method blocks of data for the user are read from the storage medium and stored in buffers of the users in successive sweeps.
The invention also relates to a system for the presentation of data from a storage medium for consumption by two or more users, which system includes a read module for reading data blocks for the user from the storage medium and for placing these blocks in buffers of the users in successive sweeps.
2. Description of the Related Art
A method and a system of this kind are known in relation to a video server, for example as described in "I/O Issues in a Multimedia System", A. L. N. Reddy and J. C. Wyllie, Computer, IEEE, March 1994, pp. 69-74. The known system includes a disc on which a number of films is stored. The system simultaneously serves a number of users and includes for each user a buffer which serves to store data read from the disc and to present data to the user. A user must receive a continuous stream of data from the video server so as to ensure continuous reproduction of the film. During so-called sweeps the system periodically reads the data required from the disc, the duration of a period being so long that during such a period for each user a block of data can be read and placed in the relevant buffer. The size of a data block is such that it contains an adequate amount of data for the relevant user for the duration of one period. In a system involving, as opposed to the known system, users which consume data from their buffers at a fixed consumption rate, the period for reading data from the disc is synchronous with the presentation of data from the buffer to the user. At the end of a period the presentation of data commences from a recently filled buffer for each user. Such a system involving users with a fixed consumption rate, therefore, does not require more than one buffer in which two blocks of data can be stored per user. In the known system, however, the consumption rate of each of the users is variable up to a given, individual maximum consumption rate. Consequently, users can reach the end of a supplied data block at mutually different instants so as to start with a new data block. The period for reading data from the disc can then no longer be synchronized with the reading of data from the buffer by the user. In that case a next sweep commences as soon as the instantaneous sweep has been completed. As a result, the strictly periodic nature of the reading of data is lost. In order to ensure a continuous stream of data to the user also in these circumstances, the known system requires a buffer in which three blocks of data can be stored for each user. It is a drawback of the known method and the known system that a comparatively large amount of storage space is required for the user buffers.